1. Field of the Invention
The present invention relates generally to systems for unloading fluids from generally upright tubular members of a wellbore. In. another aspect, the invention concerns a method and apparatus for efficiently and effectively unloading fluids from production tubing of a subterranean hydrocarbon well by utilizing a fuel cell to generate content-lifting gases in the tubing.
2. Discussion of Prior Art
In preparation for producing, and during the production of, hydrocarbons from subterranean formations, it is often necessary to unload the fluid contents of a fluid-filled production tubing string before hydrocarbon production can begin or continue. For example, certain processes either involve introducing fluid into the production tubing that must later be removed prior to production (e.g., drilling fluids, fracturing fluids, completion fluids, production fluids, etc.) or require fluids already in the production tubing to be removed (e.g., water, oil, condensate, etc.).
There are systems known in the art for unloading contents from well tubing. For example, well operators typically run coiled tubing into the well and pump the contents out of the production tubing. It is also known in the art to introduce certain gases (e.g., nitrogen) into a liquid-filled tubular to create a xe2x80x9cbubblingxe2x80x9d lifting force to assist in removing liquid from the tubing string.
These prior art systems are problematic and suffer from several limitations. For example, the coiled tubing, while effective, is inefficient as it is considerably time-consuming and requires significant additional equipment and materials to operate. Prior methods of unloading a well using gases are ineffective and may expose the formation or casing annulus to undesired elevated pressure in order to introduce sufficient gases into the well.
The present invention provides an improved system for unloading fluids from tubular members (e.g., tubing or casing) of a wellbore that does not suffer from the problems and limitations of the prior art systems as set forth above. The inventive system provides a way to effectively and efficiently unload fluids from a well tubing or casing without exposing the formation or casing to undesired elevated pressure.
In accordance with one embodiment of the present invention, a method of unloading a fluid from a generally upright tubular member of a wellbore is provided. The method comprises the steps of: (a) placing a combustible fuel cell inside the tubular member under the fluid to be unloaded; (b) burning the fuel cell to generate a gas in the tubular member; and (c) using the gas to force at least a portion of the fluid upward out of the tubular member.
In accordance with another embodiment of the present invention, an apparatus for unloading a fluid contained in a generally upright tubular member of a wellbore is provided. The apparatus generally comprises a combustible and expandable fuel cell, a cap coupled to the fuel cell, and an ignition device coupled to the fuel cell. The fuel cell is adapted to be received in the tubular member. The fuel cell defines an internal chamber which is adapted to be filled with a gas generated by the fuel cell when the fuel cell is burned. The cap is operable to hold the gas in the internal chamber until the pressure of the gas in the internal chamber causes the fuel cell to expand sufficiently to form a seal with the tubular member. The ignition device is operable to initiate burning of the fuel cell when the ignition device is actuated.
In accordance with a still further embodiment of the present invention, a wellbore extending into a subterranean formation is provided. The wellbore comprises a generally upright tubular member, a fluid disposed in the tubular member, a combustible fuel cell disposed in the tubular member generally below at least a portion of the fluid, and an ignition device coupled to the fuel cell. The fuel cell is operable to generate a gas when burned. The ignition device is operable to initiate burning of the fuel cell when the ignition device is actuated.
Other aspects and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments and the accompanying drawing figures.